The invention relates generally to gas purification systems for the purification of noble gases and nitrogen. In particular, the method of purification consists of heating an impure gas, contacting the impure gas with an impurity sorption material to produce a purified gas, cooling the purified gas to a temperature less than about 100° C., and contacting the purified gas with a hydrogen sorption material to remove residual hydrogen. The system contains an improved, low temperature hydrogen sorption and filter apparatus for substantially removing all residual hydrogen and particles from the purified gas.
In the semiconductor manufacturing industry, pure gases are used in a variety of manufacturing processes, such as chemical vapor deposition (CVD), plasma etch, etc. The purity of the gas used in the manufacturing process becomes more critical as the feature width of integrated circuits decreases. For example, more than a decade ago feature widths in the range of 3 to 5 microns were standard. Currently, integrated circuits having feature widths of less than 0.2 microns are in production. With smaller feature widths, even a very low level of contaminants can damage an integrated circuit, thereby destroying its functionality or degrading its performance. Typical contemporary process specifications require process gases to have less than 10 parts per billion (ppb) of contaminants, and preferably less than 1 ppb of contaminants.
One prior art gas purifier utilizes hot getter materials for the removal of impurities from noble gases and nitrogen. The getter materials are encased in stainless steel containers which are typically heated to a temperature in the range of 300° to 450° C. Unfortunately, stainless steel outgases a significant amount of hydrogen at temperatures above approximately 200° C. In the past when process specifications allowed 100 ppb of hydrogen in a purified process gas this was not a major problem. However, with contemporary process specifications, the hydrogen outgassed from hot stainless steel surfaces has become a significant problem.
A second vessel containing a hydrogen sorption material is typically used to remove the residual hydrogen. Briesacher et al. U.S. Pat. No. 5,238,469, issued Aug. 24, 1993 (Briesacber) discloses a typical vessel containing a hydrogen sorption material. This vessel contains a material which will sorb hydrogen from the gas flow. A separate vessel of hydrogen sorption material adds size, complexity and cost to the gas purification systems.
In addition to purification of impure gas, the gas must also be filtered to remove particles. Particles as small as 0.003 micron must be removed from the gas flow. To remove particles, dedicated particle filters are added to the outlet sections of the gas purification systems. The material utilized for the filter element is typically Teflon, but other more expensive materials such as steel may be used.
Particle filters are very precise and expensive components of the gas purification systems. In addition to cost, particle filters also add complexity and physical size to the gas purification systems. Teflon filters are temperature sensitive and cannot be operated in environments above approximately 100° C. Teflon filters can be damaged or destroyed if operated above 100° C. Teflon filters may also be contaminated with moisture or water vapor. A damaged, destroyed or contaminated filter must be replaced.
What is needed is a gas purification system which reduces the complexity, cost and physical size for equivalent purification and particle filtration performance.